In allergic disorders such as asthma and eosinophilic esophagitis (EoE), eosinophils are recruited into the lung and esophagus respectively, and activated in excess at these sites of inflammation. Eosinophils are implicated as one of the major effector cell types contributing to the pathology of these diseases. Signaling through C—C chemokine receptor 3 (CCR3), a G-protein coupled receptor (GPCR), is a critical process responsible for eosinophil recruitment.
While CCR3 is most highly expressed by eosinophils, it is also expressed by basophils, and subsets of mast cells and Th2 cells. It can be activated by a variety of chemokines including, but not limited to, the eotaxins (CCL11, CCL24, CCL26), RANTES (CCL5), MEC (CCL28), MCP-3 and MCP-4. The activation and desensitization triggered by ligand binding has not been exhaustively investigated for CCR3. However, CCR3 activation by the eotaxins and RANTES has been shown to result in calcium mobilization, activation of the MAPK/ERK1/2 and MAPK/p38 pathways, and activation of the PI3K/AKT pathway. Activation of these intracellular signaling pathways culminates in the priming, chemotaxis, activation and degranulation of the eosinophil. Concurrently, CCR3 is internalized and at least partially degraded. Eotaxin-induced CCR3 internalization has also been shown to be required for actin polymerization and chemotaxis.
The importance of CCR3 as a potential therapeutic target has been established through the observations that CCR3-null mice and eotaxin-1 and -2 double knockout mice display near complete abolishment of allergen-induced eosinophil recruitment to the airways (Fulkerson, et al. (2006) Proc. Natl. Acad. Sci. USA 103:16418-16423). There is also increased CCR3 transcript and protein levels in the bronchial mucosa of patients with allergic asthma (Ying, et al. (1997) Eur. J. Immunol. 27:3507-3516). In line with this, efforts have been made to develop small molecule CCR3 antagonists. For example, small molecule competitive inhibitors of CCR3 such as UCB35625 (1,4-trans-1-(1-Cycloocten-1-ylmethyl)-4-[[(2,7-dichloro-9H-xanthen-9-yl)carbonyl]amino]-1-ethylpiperidinium iodide), GW766994 (1-(4-acetyl-benzyl)-3-[4-(3,4-dichloro-benzyl)-morpholin-2-ylmethyl]-urea) and SB328437 (N-(1-Naphthalenylcarbonyl)-4-nitro-L-phenylalanine methyl ester) have been described. However, such molecules are typically unbiased antagonists that inhibit both chemotaxis and receptor internalization (endocytosis), leading to receptor accumulation on the cell surface. As a result, such antagonists lose their potency after prolonged administration, a phenomenon commonly referred to as drug tolerance.
Further, WO 1999/043711 and U.S. Pat. No. 7,105,488 describe monomeric CCR3 transmembrane peptides such as LLFLVTLPFWIHYVRGHNWVFGDDD (SEQ ID NO:1), FGVITSIVTWGLAVLAALPEFIFYETED (SEQ ID NO:2), IFVXMAVFFIFWTPYNVAILLSSYQSDD (SEQ ID NO:3, X=T or I), and DDLVMLVTEVIAYSHCCMNPVIYAFV (SEQ ID NO:4), which insert into a membrane in the same orientation as the transmembrane domain from which it is derived, and modulate GPCR biological activity. Peptide derivatives such as post-translational modifications and the addition of charged residues to the peptide termini are suggested to improve solubility, whereas the generation of peptidomimetics is described for increasing resistance to degradation by proteolytic enzymes.